In general, mineral slurry processing systems may be of the gravity sedimentation type or of the filter type, as discussed in the Chemical Engineers' Handbook, Fifth Edition. Sedimentation is defined as the removal of suspended solid particles from a liquor stream by gravity settling for the purposes of thickening and/or clarifying. Continuous thickener/clarifier equipment conventionally comprises a tank, a means for introducing a feed with a minimum of turbulence, a drive actuated rake mechanism for moving settled solids to a discharge point, a means for removing the thickened solids, and a means for removing the clarified liquor. Chemical and/or mechanical flocculation may be employed to remove finely divided particles from the effluent. Mechanical flocculation requires gentle circulation of the particles to provide opportunity for agglomeration by contact plus sufficient time for floc growth.
Various methods and apparatus for separating fine particle size solids from liquids are in use today. One such method and apparatus is disclosed in U.S. Pat. No. 3,523,889 to F. G. Eis. In this patent, a flocculating agent is introduced into a slurry which is then discharged from a standpipe and its flow is arrested by a baffle and deflected outwardly for mixing with the liquid in the tank. In Eis, the slurry with the flocculating agent included therein is introduced into the tank in the midst of gentle agitation. Another method is disclosed in U.S. Pat. No. 4,055,494 to R. F. Emmett, Jr. and assigned to Envirotech Corporation. In the Emmett patent, the slurry to be separated is fed successively through four mixing stages and a portion of the flocculating agent is introduced and mixed in each stage using a rotating blade. The Emmett patent does not state the type of agitation in the mixing stages. However, testimony in a trial Amstar Corporation vs. Envirotech Corporation and Energy Field Nuclear, Inc., in the U.S. District Court for the District of Utah Central Division in a division published May 3, 1983, shows that Envirotech sought to test a means of mechanically stirring flocculant and slurry with sufficient force to produce excellent floc formation but not so forceful as to destroy flocs once formed. J. Rosenbau, & J. Clemmer, "Liquid-Solids Separations," in J. Clegg & D. Foley, Uranium Ore Processing 172, 1980 (1958), ("the flocculant must be disseminated uniformly throughout the slurry without degrading the floccules. Intense agitation to distribute the reagent for maximum effectiveness degrades the fragile floccules, and thus defeats its own purpose.") The process in each of Eis and Emmett forms generally butterfly-like floccules which tend to result in cake which is relatively wet and sticky when separated out of the slurry.